public function testValidator() { $collection = new Collection(['a', 'b', 'c']); $collection->addValidator($validator = function ($value) { return strlen($value) == 1; }); $this->assertAttributeEquals(Collection::cast([$validator]), 'validators', $collection); $this->expectsException(function () use($collection) { $collection[] = 'invalid string!'; }, Exception::class); }